This is different from the Unicode definition in chapter 3.5, conformance clause D13, which defines base characters
to be all characters (not Cn) that do not graphically combine with preceding characters (M) and that are neither
control (Cc) or format (Cf) characters.

Parameters

codepoint

The integer codepoint value (e.g. 0x2603 for U+2603 SNOWMAN), or the character encoded as a UTF-8 string (e.g. "\u{2603}")